Travel. Especially the CA schools, they care much less about athletics even though football/basketball are good revenue sports. If a team like BYU were to join, they would be 50/50 splits at best fan wise and these presidents would have to address the issue to appease the alumni. With no BYU, it’s just an empty stadium and it looks conference wide (and the oregons, utahs, ASU’s don’t want to go to Stanford, cal, SC, etc because they’d prefer a better environment). Yes, then the religious aspect.
As you can tell by my presence here, I would rather mix it up with other fans than to have three apathetic Stanford fans at the game. I go to the ASU game every year with a former player. Went to SDSU with a former player. Love the Oregon crowds at Utah. Typically try to make it to LES for Utah-BYU. Most Californians just think they’re too good to be challenged by anyone else